A polymer-based material, for example, a silicone rubber or polyurethane, is widely used as a medical material such as a percutance trans-catheter, because of its bioinertness, long-term stability, strength, flexibility etc. However, since the polymer-based material with bioinertness does not adhere to the dermal living organism, it commonly causes a risk of Down-growth (a phenomenon in which epithelial tissue invaginate into the skin along the surface of the catheter), and a risk of bacterial infection of the invaginate portion.
Meanwhile, calcium phosphate, for example, a hydroxyapatite, is also widely used as a bioactive material in the medical field as such, or as a complex with an inorganic material or an organic material. Percutaneous trans-catheter is one of applications of such a calcium phosphate. However, the calcium phosphate is fragile, poor in formability, and has no affinity to a metal material. Therefore, when the calcium phosphate is used for a percutaneous trans-catheter, it may cause bacterial infection via the gap between the metal material and the calcium phosphate terminal.
In view of this problem, a hydroxyapatite complex has been suggested. The hydroxyapatite complex is made of a polymer-based material whose surface is modified by calcium phosphate such as hydroxyapatite.
To modify the surface of a polymer-based material by calcium phosphate, some different methods have been disclosed, for example, a modification method using sputtering ion beam (Document 1: Japanese Laid-Open Patent Application Tokukaihei 08-56963/1996, published on Mar. 5, 1996), a modification method using plasma treatment (Document 2: Japanese Laid-Open Patent Application Tokukaihei 07-303691/1996, published on Nov. 21, 1995), a modification method by complexation with glass (Document 3: Japanese Laid-Open Patent Application Tokukaisho 63-270061/1988, published on Nov. 8, 1988), a modification method using vital imitation reaction (Document 4: Japanese Laid-Open Patent Application Tokukaisho 07-306201/1995, published on Nov. 21, 1995), and a modification method using alternate immersion (Document 5: Japanese Laid-Open Patent Application Tokukai 2000-342676/2000, published on Dec. 12, 2000).
However, since the calcium phosphate used in the modification methods of the foregoing publications has an amorphous structure, it is easily dissolved in a living body. Therefore, this calcium phosphate is not desirable in terms of persistence of bioactivity. Accordingly, the calcium phosphate is suitable for a usage in which the calcium phosphate is dissolved in a living body (for example, a bone-substitution material), but not suitable for a usage in which the calcium phosphate is kept in the body for a long-period (for example, percutance terminal). Further, in the modification methods disclosed in the foregoing publications, the calcium phosphate is physically or electrostatically fixed into the base-material, which does not ensure sufficient strength in adherence.
In this view, there has been a demand for alternative method for modifying the surface of the polymer-based material by the calcium phosphate for the usage where the calcium phosphate is kept in a body for a long-period. An alternative to solve this problem can be found in Document 6 (Japanese Laid-Open Patent Application Tokukaihei 10-15061/1998, published on Jan. 20, 1998) or Document 7 (Japanese Laid-Open Patent Application Tokukai 2001-172511/2001, published on Jun. 26, 2001).
The Document 6 discloses an intraperitoneal indwelling catheter, which is created by fixing ceramic porous particles to the surface of the polymer-based material by an adhesive, or by fusing the polymer-based material so that the ceramic porous particles are fixed on the surface.
However, in the method of Document 6, the ceramic porous particles are physically fixed into the base-material, and therefore it cannot ensure strength in adherence.
Further, in the method of fixing the ceramic porous particles into the surface of the polymer-based material by an adhesive, the ceramic porous particles may be laminated on the surface of the polymer-based material. This may cause ruin of physicality of the polymer-based material, or elution of the adhesive.
Further, in the method of fusing the polymer-based material so that the ceramic porous particles are fixed to the surface, body fat may permeate into the polymer-based material via the fixing portion, which can ruin physicality of the polymer-based material.
Further, the method of Document 7 requires a chemical pre-treatment to introduce an active group into the calcium phosphate.
In the presence of such problems, there is a demand for an alternative method for modifying the polymer-based material by the calcium phosphate which enables the calcium phosphate to be easily fixed to the surface of the polymer-based material for a long period without loosing bioactivity, as well as a demand for a calcium phosphate complex (hydroxyapatite complex) obtained by the method.